Method and apparatus for generating stf signal using binary sequence in wireless lan system

ABSTRACT

Disclosed are a method and an apparatus for generating an STF signal usable in a wireless LAN system. The STF signal is included in a field used to improve AGC estimation of a MIMO transmission. A portion of the STF signal is used to transmit an uplink, and can be used for uplink MU PPDUs transmitted from a plurality of STAs. The STF that is suggested, for example, is used for a 40 MHz band or an 80 MHz band and can be generated based on a sequence in which a predetermined M sequence is repeated. The predetermined M sequence can be a binary sequence of which the length is 15 bits.

BACKGROUND OF THE INVENTION Field of the Invention

This specification relates to a method for generating a sequence for atraining field in a wireless LAN system and, most particularly, to amethod and apparatus for generating a short training field (STF)sequence that can be used in multiple bands in a wireless LAN system.

Related Art

Discussion for a next-generation wireless local area network (WLAN) isin progress. In the next-generation WLAN, an object is to 1) improve aninstitute of electronic and electronics engineers (IEEE) 802.11 physical(PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHzand 5 GHz, 2) increase spectrum efficiency and area throughput, 3)improve performance in actual indoor and outdoor environments such as anenvironment in which an interference source exists, a denseheterogeneous network environment, and an environment in which a highuser load exists, and the like.

An environment which is primarily considered in the next-generation WLANis a dense environment in which access points (APs) and stations (STAs)are a lot and under the dense environment, improvement of the spectrumefficiency and the area throughput is discussed. Further, in thenext-generation WLAN, in addition to the indoor environment, in theoutdoor environment which is not considerably considered in the existingWLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned in thenext-generation WLAN and discussion about improvement of systemperformance in a dense environment in which the APs and the STAs are alot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are anticipatedto be actively discussed rather than improvement of single linkperformance in one basic service set (BSS). Directionality of thenext-generation means that the next-generation WLAN gradually has atechnical scope similar to mobile communication. When a situation isconsidered, in which the mobile communication and the WLAN technologyhave been discussed in a small cell and a direct-to-direct (D2D)communication area in recent years, technical and business convergenceof the next-generation WLAN and the mobile communication is predicted tobe further active.

SUMMARY OF THE INVENTION Technical Objects

This specification proposes a method and apparatus for configuring asequence that is used for a training field in a wireless LAN system.

An example of this specification proposes a solution for enhancing theproblems in the sequence for the STF field that is presented in therelated art.

Technical Solutions

An example of this specification proposes a transmission method that canbe applied to a wireless LAN system and, most particularly, to a methodand apparatus for configuring a STF signal supporting at least any oneof multiple frequency bands supported by the wireless LAN system.

A transmitting apparatus according to the example of the presentinvention generates a short training field (STF) signal corresponding tothe first frequency band and transmits a physical protocol data unit(PPDU) including the STF signal.

The STF signal corresponding to the first frequency band may begenerated based on a sequence in which a predetermined M sequence isrepeated.

The repeated sequence may be defined as {M, −1, M, −1, −M, −1, M, 0, −M,1, M, 1, −M, 1, −M}*(1+j)/sqrt(2).

The predetermined M sequence may correspond to a binary sequence havinga length of 15 bits. In this case, the M sequence may correspond toM={−1, −1, −1, 1, 1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}.

EFFECTS OF THE INVENTION

According to an example of this specification, a method for generating aSTF signal that can be used in the wireless LAN system is proposedherein.

The method for generating a STF signal that is proposed in the exampleof this specification resolves the problems presented in the relatedart.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

FIG. 9 illustrates an example of a trigger frame.

FIG. 10 illustrates an example of a common information field.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field.

FIG. 12 is a block diagram illustrating an example of an uplink MU PPDU.

FIG. 13 illustrates a 1× HE-STF tone in a per-channel PPDU transmissionaccording to an exemplary embodiment of the present invention.

FIG. 14 illustrates a 2× HE-STF tone in a per-channel PPDU transmissionaccording to an exemplary embodiment of the present invention.

FIG. 15 illustrates an example of repeating an M sequence.

FIG. 16 is an example specifying the repeated structure of FIG. 15 inmore detail.

FIG. 17 illustrates an example of repeating an M sequence.

FIG. 18 is an example specifying the repeated structure of FIG. 17 inmore detail.

FIG. 19 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 20 MHz band.

FIG. 20 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 40 MHz band.

FIG. 21 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a left side band of a 80 MHz band.

FIG. 22 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a right side band of a 80 MHz band.

FIG. 23 illustrates an example of repeating an M sequence.

FIG. 24 is an example specifying the repeated structure of FIG. 23 inmore detail.

FIG. 25 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 20 MHz band.

FIG. 26 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 40 MHz band.

FIG. 27 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a left side band of a 80 MHz band.

FIG. 28 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a right side band of a 80 MHz band.

FIG. 29 is a procedure flow chart to which the above-described examplecan be applied.

FIG. 30 is a block view showing a wireless device to which the exemplaryembodiment of the present invention can be applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructurebasic service set (BSS) of institute of electrical and electronicengineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may includeone or more infrastructure BSSs 100 and 105 (hereinafter, referred to asBSS). The BSSs 100 and 105 as a set of an AP and an STA such as anaccess point (AP) 125 and a station (STA1) 100-1 which are successfullysynchronized to communicate with each other are not concepts indicatinga specific region. The BSS 105 may include one or more STAs 105-1 and105-2 which may be joined to one AP 130.

The BSS may include at least one STA, APs providing a distributionservice, and a distribution system (DS) 110 connecting multiple APs.

The distribution system 110 may implement an extended service set (ESS)140 extended by connecting the multiple BSSs 100 and 105. The ESS 140may be used as a term indicating one network configured by connectingone or more APs 125 or 230 through the distribution system 110. The APincluded in one ESS 140 may have the same service set identification(SSID).

A portal 120 may serve as a bridge which connects the wireless LANnetwork (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network betweenthe APs 125 and 130 and a network between the APs 125 and 130 and theSTAs 100-1, 105-1, and 105-2 may be implemented. However, the network isconfigured even between the STAs without the APs 125 and 130 to performcommunication. A network in which the communication is performed byconfiguring the network even between the STAs without the APs 125 and130 is defined as an Ad-Hoc network or an independent basic service set(IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating theIBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operatesin an Ad-Hoc mode. Since the IBSS does not include the access point(AP), a centralized management entity that performs a managementfunction at the center does not exist. That is, in the IBSS, STAs 150-1,150-2, 150-3, 155-4, and 155-5 are managed by a distributed manner. Inthe IBSS, all STAs 150-1, 150-2, 150-3, 155-4, and 155-5 may beconstituted by movable STAs and are not permitted to access the DS toconstitute a self-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

Meanwhile, the term user may be used in diverse meanings, for example,in wireless LAN communication, this term may be used to signify a STAparticipating in uplink MU MIMO and/or uplink OFDMA transmission.However, the meaning of this term will not be limited only to this.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

As illustrated in FIG. 2, various types of PHY protocol data units(PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. In detail,LTF and STF fields include a training signal, SIG-A and SIG-B includecontrol information for a receiving station, and a data field includesuser data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which isassociated with a signal (alternatively, a control information field)used for the data field of the PPDU. The signal provided in theembodiment may be applied onto high efficiency PPDU (HE PPDU) accordingto an IEEE 802.11ax standard. That is, the signal improved in theembodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. TheHE-SIG-A and the HE-SIG-B may be represented even as the SIG-A andSIG-B, respectively. However, the improved signal proposed in theembodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-Bstandard and may be applied to control/data fields having various names,which include the control information in a wireless communication systemtransferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be theHE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is oneexample of the PPDU for multiple users and only the PPDU for themultiple users may include the HE-SIG-B and the corresponding HE SIG-Bmay be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted during an illustrated time period (that is, 4 or 8 μs).

More detailed description of the respective fields of FIG. 3 will bemade below.

FIG. 4 is a diagram illustrating a layout of resource units (RUs) usedin a band of 20 MHz.

As illustrated in FIG. 4, resource units (RUs) corresponding to tone(that is, subcarriers) of different numbers are used to constitute somefields of the HE-PPDU. For example, the resources may be allocated bythe unit of the RU illustrated for the HE-STF, the HE-LTF, and the datafield.

As illustrated in an uppermost part of FIG. 4, 26 units (that is, unitscorresponding to 26 tones). 6 tones may be used as a guard band in aleftmost band of the 20 MHz band and 5 tones may be used as the guardband in a rightmost band of the 20 MHz band. Further, 7 DC tones may beinserted into a center band, that is, a DC band and a 26-unitcorresponding to each 13 tones may be present at left and right sides ofthe DC band. The 26-unit, a 52-unit, and a 106-unit may be allocated toother bands. Each unit may be allocated for a receiving station, thatis, a user.

Meanwhile, the RU layout of FIG. 4 may be used even in a situation for asingle user (SU) in addition to the multiple users (MUs) and in thiscase, as illustrated in a lowermost part of FIG. 4, one 242-unit may beused and in this case, three DC tones may be inserted.

In one example of FIG. 4, RUs having various sizes, that is, a 26-RU, a52-RU, a 106-RU, a 242-RU, and the like are proposed, and as a result,since detailed sizes of the RUs may extend or increase, the embodimentis not limited to a detailed size (that is, the number of correspondingtones) of each RU.

FIG. 5 is a diagram illustrating a layout of resource units (RUs) usedin a band of 40 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of FIG. 4, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and the likemay be used even in one example of FIG. 5. Further, 5 DC tones may beinserted into a center frequency, 12 tones may be used as the guard bandin the leftmost band of the 40 MHz band and 11 tones may be used as theguard band in the rightmost band of the 40 MHz band.

In addition, as illustrated in FIG. 5, when the RU layout is used forthe single user, the 484-RU may be used. That is, the detailed number ofRUs may be modified similarly to one example of FIG. 4.

FIG. 6 is a diagram illustrating a layout of resource units (RUs) usedin a band of 80 MHz.

Similarly to a case in which the RUs having various RUs are used in oneexample of each of FIG. 4 or 5, 26-RU, 52-RU, 106-RU, 242-RU, 484-RU,and the like may be used even in one example of FIG. 6. Further, 7 DCtones may be inserted into the center frequency, 12 tones may be used asthe guard band in the leftmost band of the 80 MHz band and 11 tones maybe used as the guard band in the rightmost band of the 80 MHz band. Inaddition, the 26-RU may be used, which uses 13 tones positioned at eachof left and right sides of the DC band.

Moreover, as illustrated in FIG. 6, when the RU layout is used for thesingle user, 996-RU may be used and in this case, 5 DC tones may beinserted. Meanwhile, the detailed number of RUs may be modifiedsimilarly to one example of each of FIG. 4 or 5.

FIG. 7 is a diagram illustrating another example of the HE PPDU.

A block illustrated in FIG. 7 is another example of describing theHE-PPDU block of FIG. 3 in terms of a frequency.

An illustrated L-STF 700 may include a short training orthogonalfrequency division multiplexing (OFDM) symbol. The L-STF 700 may be usedfor frame detection, automatic gain control (AGC), diversity detection,and coarse frequency/time synchronization.

An L-LTF 710 may include a long training orthogonal frequency divisionmultiplexing (OFDM) symbol. The L-LTF 710 may be used for finefrequency/time synchronization and channel prediction.

An L-SIG 720 may be used for transmitting control information. The L-SIG720 may include information regarding a data rate and a data length.Further, the L-SIG 720 may be repeatedly transmitted. That is, a newformat, in which the L-SIG 720 is repeated (for example, may be referredto as R-LSIG) may be configured.

An HE-SIG-A 730 may include the control information common to thereceiving station.

In detail, the HE-SIG-A 730 may include information on 1) a DL/ULindicator, 2) a BSS color field indicating an identify of a BSS, 3) afield indicating a remaining time of a current TXOP period, 4) abandwidth field indicating at least one of 20, 40, 80, 160 and 80+80MHz, 5) a field indicating an MCS technique applied to the HE-SIG-B, 6)an indication field regarding whether the HE-SIG-B is modulated by adual subcarrier modulation technique for MCS, 7) a field indicating thenumber of symbols used for the HE-SIG-B, 8) a field indicating whetherthe HE-SIG-B is configured for a full bandwidth MIMO transmission, 9) afield indicating the number of symbols of the HE-LTF, 10) a fieldindicating the length of the HE-LTF and a CP length, 11) a fieldindicating whether an OFDM symbol is present for LDPC coding, 12) afield indicating control information regarding packet extension (PE),13) a field indicating information on a CRC field of the HE-SIG-A, andthe like. A detailed field of the HE-SIG-A may be added or partiallyomitted. Further, some fields of the HE-SIG-A may be partially added oromitted in other environments other than a multi-user (MU) environment.

An HE-SIG-B 740 may be included only in the case of the PPDU for themultiple users (MUs) as described above. Principally, an HE-SIG-A 750 oran HE-SIG-B 760 may include resource allocation information(alternatively, virtual resource allocation information) for at leastone receiving STA.

FIG. 8 is a block diagram illustrating one example of HE-SIG-B accordingto an embodiment.

As illustrated in FIG. 8, the HE-SIG-B field includes a common field ata frontmost part and the corresponding common field is separated from afield which follows therebehind to be encoded. That is, as illustratedin FIG. 8, the HE-SIG-B field may include a common field including thecommon control information and a user-specific field includinguser-specific control information. In this case, the common field mayinclude a CRC field corresponding to the common field, and the like andmay be coded to be one BCC block. The user-specific field subsequentthereafter may be coded to be one BCC block including the “user-specificfield” for 2 users and a CRC field corresponding thereto as illustratedin FIG. 8.

A previous field of the HE-SIG-B 740 may be transmitted in a duplicatedform on an MU PPDU. In the case of the HE-SIG-B 740, the HE-SIG-B 740transmitted in some frequency band (e.g., a fourth frequency band) mayeven include control information for a data field corresponding to acorresponding frequency band (that is, the fourth frequency band) and adata field of another frequency band (e.g., a second frequency band)other than the corresponding frequency band. Further, a format may beprovided, in which the HE-SIG-B 740 in a specific frequency band (e.g.,the second frequency band) is duplicated with the HE-SIG-B 740 ofanother frequency band (e.g., the fourth frequency band). Alternatively,the HE-SIG B 740 may be transmitted in an encoded form on alltransmission resources. A field after the HE-SIG B 740 may includeindividual information for respective receiving STAs receiving the PPDU.

The HE-STF 750 may be used for improving automatic gain controlestimation in a multiple input multiple output (MIMO) environment or anOFDMA environment.

The HE-LTF 760 may be used for estimating a channel in the MIMOenvironment or the OFDMA environment.

The size of fast Fourier transform (FFT)/inverse fast Fourier transform(IFFT) applied to the HE-STF 750 and the field after the HE-STF 750, andthe size of the FFT/IFFT applied to the field before the HE-STF 750 maybe different from each other. For example, the size of the FFT/IFFTapplied to the HE-STF 750 and the field after the HE-STF 750 may be fourtimes larger than the size of the FFT/IFFT applied to the field beforethe HE-STF 750.

For example, when at least one field of the L-STF 700, the L-LTF 710,the L-SIG 720, the HE-SIG-A 730, and the HE-SIG-B 740 on the PPDU ofFIG. 7 is referred to as a first field, at least one of the data field770, the HE-STF 750, and the HE-LTF 760 may be referred to as a secondfield. The first field may include a field associated with a legacysystem and the second field may include a field associated with an HEsystem. In this case, the fast Fourier transform (FFT) size and theinverse fast Fourier transform (IFFT) size may be defined as a sizewhich is N (N is a natural number, e.g., N=1, 2, and 4) times largerthan the FFT/IFFT size used in the legacy wireless LAN system. That is,the FFT/IFFT having the size may be applied, which is N (=4) timeslarger than the first field of the HE PPDU. For example, 256 FFT/IFFTmay be applied to a bandwidth of 20 MHz, 512 FFT/IFFT may be applied toa bandwidth of 40 MHz, 1024 FFT/IFFT may be applied to a bandwidth of 80MHz, and 2048 FFT/IFFT may be applied to a bandwidth of continuous 160MHz or discontinuous 160 MHz.

In other words, a subcarrier space/subcarrier spacing may have a sizewhich is 1/N times (N is the natural number, e.g., N=4, the subcarrierspacing is set to 78.125 kHz) the subcarrier space used in the legacywireless LAN system. That is, subcarrier spacing having a size of 312.5kHz, which is legacy subcarrier spacing may be applied to the firstfield of the HE PPDU and a subcarrier space having a size of 78.125 kHzmay be applied to the second field of the HE PPDU.

Alternatively, an IDFT/DFT period applied to each symbol of the firstfield may be expressed to be N(=4) times shorter than the IDFT/DFTperiod applied to each data symbol of the second field. That is, theIDFT/DFT length applied to each symbol of the first field of the HE PPDUmay be expressed as 3.2 μs and the IDFT/DFT length applied to eachsymbol of the second field of the HE PPDU may be expressed as 3.2μs*4(=12.8 μs). The length of the OFDM symbol may be a value acquired byadding the length of a guard interval (GI) to the IDFT/DFT length. Thelength of the GI may have various values such as 0.4 μs, 0.8 μs, 1.6 μs,2.4 μs, and 3.2 μs.

The characteristic that the size of the FFT/IFFT being applied to theHE-STF 750 and the fields after the HE-STF 750 can be diverselyconfigured may be applied to a downlink PPDU and/or an uplink PPDU. Morespecifically, such characteristic may be applied to the PPDU shown inFIG. 7 or to an uplink MU PPDU, which will be described later on.

For simplicity in the description, in FIG. 7, it is expressed that afrequency band used by the first field and a frequency band used by thesecond field accurately coincide with each other, but both frequencybands may not completely coincide with each other, in actual. Forexample, a primary band of the first field (L-STF, L-LTF, L-SIG,HE-SIG-A, and HE-SIG-B) corresponding to the first frequency band may bethe same as the most portions of a frequency band of the second field(HE-STF, HE-LTF, and Data), but boundary surfaces of the respectivefrequency bands may not coincide with each other. As illustrated inFIGS. 4 to 6, since multiple null subcarriers, DC tones, guard tones,and the like are inserted during arranging the RUs, it may be difficultto accurately adjust the boundary surfaces.

The user (e.g., a receiving station) may receive the HE-SIG-A 730 andmay be instructed to receive the downlink PPDU based on the HE-SIG-A730. In this case, the STA may perform decoding based on the FFT sizechanged from the HE-STF 750 and the field after the HE-STF 750. On thecontrary, when the STA may not be instructed to receive the downlinkPPDU based on the HE-SIG-A 730, the STA may stop the decoding andconfigure a network allocation vector (NAV). A cyclic prefix (CP) of theHE-STF 750 may have a larger size than the CP of another field and theduring the CP period, the STA may perform the decoding for the downlinkPPDU by changing the FFT size.

Hereinafter, in the embodiment of the present invention, data(alternatively, or a frame) which the AP transmits to the STA may beexpressed as a terms called downlink data (alternatively, a downlinkframe) and data (alternatively, a frame) which the STA transmits to theAP may be expressed as a term called uplink data (alternatively, anuplink frame). Further, transmission from the AP to the STA may beexpressed as downlink transmission and transmission from the STA to theAP may be expressed as a term called uplink transmission.

In addition, a PHY protocol data unit (PPDU), a frame, and datatransmitted through the downlink transmission may be expressed as termssuch as a downlink PPDU, a downlink frame, and downlink data,respectively. The PPDU may be a data unit including a PPDU header and aphysical layer service data unit (PSDU) (alternatively, a MAC protocoldata unit (MPDU)). The PPDU header may include a PHY header and a PHYpreamble and the PSDU (alternatively, MPDU) may include the frame orindicate the frame (alternatively, an information unit of the MAC layer)or be a data unit indicating the frame. The PHY header may be expressedas a physical layer convergence protocol (PLCP) header as another termand the PHY preamble may be expressed as a PLCP preamble as anotherterm.

Further, a PPDU, a frame, and data transmitted through the uplinktransmission may be expressed as terms such as an uplink PPDU, an uplinkframe, and uplink data, respectively.

In the wireless LAN system to which the embodiment of the presentdescription is applied, the whole bandwidth may be used for downlinktransmission to one STA and uplink transmission to one STA. Further, inthe wireless LAN system to which the embodiment of the presentdescription is applied, the AP may perform downlink (DL) multi-user (MU)transmission based on multiple input multiple output (MU MIMO) and thetransmission may be expressed as a term called DL MU MIMO transmission.

In addition, in the wireless LAN system according to the embodiment, anorthogonal frequency division multiple access (OFDMA) based transmissionmethod is preferably supported for the uplink transmission and/ordownlink transmission. That is, data units (e.g., RUs) corresponding todifferent frequency resources are allocated to the user to performuplink/downlink communication. In detail, in the wireless LAN systemaccording to the embodiment, the AP may perform the DL MU transmissionbased on the OFDMA and the transmission may be expressed as a termcalled DL MU OFDMA transmission. When the DL MU OFDMA transmission isperformed, the AP may transmit the downlink data (alternatively, thedownlink frame and the downlink PPDU) to the plurality of respectiveSTAs through the plurality of respective frequency resources on anoverlapped time resource. The plurality of frequency resources may be aplurality of subbands (alternatively, sub channels) or a plurality ofresource units (RUs). The DL MU OFDMA transmission may be used togetherwith the DL MU MIMO transmission. For example, the DL MU MIMOtransmission based on a plurality of space-time streams (alternatively,spatial streams) may be performed on a specific subband (alternatively,sub channel) allocated for the DL MU OFDMA transmission.

Further, in the wireless LAN system according to the embodiment, uplinkmulti-user (UL MU) transmission in which the plurality of STAs transmitsdata to the AP on the same time resource may be supported. Uplinktransmission on the overlapped time resource by the plurality ofrespective STAs may be performed on a frequency domain or a spatialdomain.

When the uplink transmission by the plurality of respective STAs isperformed on the frequency domain, different frequency resources may beallocated to the plurality of respective STAs as uplink transmissionresources based on the OFDMA. The different frequency resources may bedifferent subbands (alternatively, sub channels) or different resourcesunits (RUs). The plurality of respective STAs may transmit uplink datato the AP through different frequency resources. The transmission methodthrough the different frequency resources may be expressed as a termcalled a UL MU OFDMA transmission method.

When the uplink transmission by the plurality of respective STAs isperformed on the spatial domain, different time-space streams(alternatively, spatial streams) may be allocated to the plurality ofrespective STAs and the plurality of respective STAs may transmit theuplink data to the AP through the different time-space streams. Thetransmission method through the different spatial streams may beexpressed as a term called a UL MU MIMO transmission method.

The UL MU OFDMA transmission and the UL MU MIMO transmission may be usedtogether with each other. For example, the UL MU MIMO transmission basedon the plurality of space-time streams (alternatively, spatial streams)may be performed on a specific subband (alternatively, sub channel)allocated for the UL MU OFDMA transmission.

In the legacy wireless LAN system which does not support the MU OFDMAtransmission, a multi-channel allocation method is used for allocating awider bandwidth (e.g., a 20 MHz excess bandwidth) to one terminal. Whena channel unit is 20 MHz, multiple channels may include a plurality of20 MHz-channels. In the multi-channel allocation method, a primarychannel rule is used to allocate the wider bandwidth to the terminal.When the primary channel rule is used, there is a limit for allocatingthe wider bandwidth to the terminal. In detail, according to the primarychannel rule, when a secondary channel adjacent to a primary channel isused in an overlapped BSS (OBSS) and is thus busy, the STA may useremaining channels other than the primary channel. Therefore, since theSTA may transmit the frame only to the primary channel, the STA receivesa limit for transmission of the frame through the multiple channels.That is, in the legacy wireless LAN system, the primary channel ruleused for allocating the multiple channels may be a large limit inobtaining a high throughput by operating the wider bandwidth in acurrent wireless LAN environment in which the OBSS is not small.

In order to solve the problem, in the embodiment, a wireless LAN systemis disclosed, which supports the OFDMA technology. That is, the OFDMAtechnique may be applied to at least one of downlink and uplink.Further, the MU-MIMO technique may be additionally applied to at leastone of downlink and uplink. When the OFDMA technique is used, themultiple channels may be simultaneously used by not one terminal butmultiple terminals without the limit by the primary channel rule.Therefore, the wider bandwidth may be operated to improve efficiency ofoperating a wireless resource.

As described above, in case the uplink transmission performed by each ofthe multiple STAs (e.g., non-AP STAs) is performed within the frequencydomain, the AP may allocate different frequency resources respective toeach of the multiple STAs as uplink transmission resources based onOFDMA. Additionally, as described above, the frequency resources eachbeing different from one another may correspond to different subbands(or sub-channels) or different resource units (RUs).

The different frequency resources respective to each of the multipleSTAs are indicated through a trigger frame.

FIG. 9 illustrates an example of a trigger frame. The trigger frame ofFIG. 9 allocates resources for Uplink Multiple-User (MU) transmissionand may be transmitted from the AP. The trigger frame may be configuredas a MAC frame and may be included in the PPDU. For example, the triggerframe may be transmitted through the PPDU shown in FIG. 3, through thelegacy PPDU shown in FIG. 2, or through a certain PPDU, which is newlydesigned for the corresponding trigger frame. In case the trigger frameis transmitted through the PPDU of FIG. 3, the trigger frame may beincluded in the data field shown in the drawing.

Each of the fields shown in FIG. 9 may be partially omitted, or otherfields may be added. Moreover, the length of each field may be varieddifferently as shown in the drawing.

A Frame Control field 910 shown in FIG. 9 may include informationrelated to a version of the MAC protocol and other additional controlinformation, and a Duration field 920 may include time information forconfiguring a NAV or information related to an identifier (e.g., AID) ofthe user equipment.

Additionally, a RA field 930 may include address information of areceiving STA of the corresponding trigger frame, and this field mayalso be omitted as required. A TA field 940 may include addressinformation of the STA (e.g., AP) transmitting the corresponding triggerframe, and a common information field 950 may include common controlinformation that is applied to the receiving STA receiving thecorresponding trigger frame.

FIG. 10 illustrates an example of a common information field. Among thesub-fields of FIG. 10, some may be omitted, and other additionalsub-fields may also be added. Additionally, the length of each of thesub-fields shown in the drawing may be varied.

As shown in the drawing, the Length field1010 may be given that samevalue as the Length field of the L-SIG field of the uplink PPDU, whichis transmitted in response to the corresponding trigger frame, and theLength field of the L-SIG field of the uplink PPDU indicates the lengthof the uplink PPDU. As a result, the Length field 1010 of the triggerframe may be used for indicating the length of its respective uplinkPPDU.

Additionally, a Cascade Indicator field 1020 indicates whether or not acascade operation is performed. The cascade operation refers to adownlink MU transmission and an uplink MU transmission being performedsimultaneously within the same TXOP. More specifically, this refers to acase when a downlink MU transmission is first performed, and, then,after a predetermined period of time (e.g., SIFS), an uplink MUtransmission is performed. During the cascade operation, only onetransmitting device performing downlink communication (e.g., AP) mayexist, and multiple transmitting devices performing uplink communication(e.g., non-AP) may exist.

A CS Request field 1030 indicates whether or not the status or NAV of awireless medium is required to be considered in a situation where areceiving device that has received the corresponding trigger frametransmits the respective uplink PPDU.

A HE-SIG-A information field 1040 may include information controllingthe content of a SIG-A field (i.e., HE-SIG-A field) of an uplink PPDU,which is being transmitted in response to the corresponding triggerframe.

A CP and LTF type field 1050 may include information on a LTF length anda CP length of the uplink PPDU being transmitted in response to thecorresponding trigger frame. A trigger type field 1060 may indicate apurpose for which the corresponding trigger frame is being used, e.g.,general triggering, triggering for beamforming, and so on, a request fora Block ACK/NACK, and so on.

Meanwhile, the remaining description on FIG. 9 will be additionallyprovided as described below.

It is preferable that the trigger frame includes per user informationfields 960#1 to 960#N corresponding to the number of receiving STAsreceiving the trigger frame of FIG. 9. The per user information fieldmay also be referred to as a “RU Allocation field”.

Additionally, the trigger frame of FIG. 9 may include a Padding field970 and a Sequence field 980.

It is preferable that each of the per user information fields 960#1 to960#N shown in FIG. 9 further includes multiple sub-fields.

FIG. 11 illustrates an example of a sub-field being included in a peruser information field. Among the sub-fields of FIG. 11, some may beomitted, and other additional sub-fields may also be added.Additionally, the length of each of the sub-fields shown in the drawingmay be varied.

A User Identifier field 1110 indicates an identifier of an STA (i.e.,receiving STA) to which the per user information corresponds, and anexample of the identifier may correspond to all or part of the AID.

Additionally, a RU Allocation field 1120 may be included in thesub-field of the per user information field. More specifically, in casea receiving STA, which is identified by the User Identifier field 1110,transmits an uplink PPDU in response to the trigger frame of FIG. 9, thecorresponding uplink PPDU is transmitted through the RU, which isindicated by the RU Allocation field 1120. In this case, it ispreferable that the RU that is being indicated by the RU Allocationfield 1120 corresponds to the RU shown in FIG. 4, FIG. 5, and FIG. 6.

The sub-field of FIG. 11 may include a Coding Type field 1130. TheCoding Type field 1130 may indicate a coding type of the uplink PPDUbeing transmitted in response to the trigger frame of FIG. 9. Forexample, in case BBC coding is applied to the uplink PPDU, the CodingType field 1130 may be set to ‘1’, and, in case LDPC coding is appliedto the uplink PPDU, the Coding Type field 1130 may be set to ‘0’.

Additionally, the sub-field of FIG. 11 may include a MCS field 1140. TheMCS field 1140 may indicate a MCS scheme being applied to the uplinkPPDU that is transmitted in response to the trigger frame of FIG. 9. Forexample, in case BBC coding is applied to the uplink PPDU, the CodingType field 1130 may be set to ‘1’, and, in case LDPC coding is appliedto the uplink PPDU, the Coding Type field 1130 may be set to ‘0’.

FIG. 12 is a block diagram illustrating an example of an uplink MU PPDU.The uplink MU PPDU of FIG. 12 may be transmitted in response to theabove-described trigger frame.

As shown in the drawing, the PPDU of FIG.12 includes diverse fields, andthe fields included herein respectively correspond to the fields shownin FIG. 2, FIG. 3, and FIG. 7. Meanwhile, as shown in the drawing, theuplink PPDU of FIG. 12 may not include a HE-SIG-B field and may onlyinclude a HE-SIG-A field.

FIG. 13 illustrates a 1× HE-STF tone in a per-channel PPDU transmissionaccording to an exemplary embodiment of the present invention. Mostparticularly, FIG. 13 shows an example of a HE-STF tone (i.e., 16-tonesampling) having a periodicity of 0.8 μs in 20 MHz/40 MHz/80 MHzbandwidths. Accordingly, in FIG. 13, the HE-STF tones for each bandwidth(or channel) may be positioned at 16 tone intervals.

In FIG. 13, the x-axis represents the frequency domain The numbers onthe x-axis represent the indexes of a tone, and the arrows representmapping of a value that is not equal to 0 (i.e., a non-zero value) tothe corresponding tone index.

Sub-drawing (a) of FIG. 13 illustrates an example of a 1× HE-STF tone ina 20 MHz PPDU transmission.

Referring to sub-drawing (a), in case a HE-STF sequence (i.e., 1×HE-STFsequence) for a periodicity of 0.81 μs is mapped to tones of a 20 MHzchannel, the 1× HE-STF sequence is mapped to tones having tone indexesthat are divisible by 16 (i.e., multiples of 16), among the tones havingtone indexes ranging from −112 to 112, and, then, 0 may be mapped to theremaining tones. More specifically, in a 20 MHz channel, among the toneshaving tone indexes ranging from −112 to 112, a 1× HE-STF tone may bepositioned at a tone index that is divisible by 16 excluding the DC.Accordingly, a total of 14 1 HE-STF tones having the 133 HE-STF sequencemapped thereto may exist in the 20 MHz channel.

Sub-drawing (b) of FIG. 13 illustrates an example of a 1× HE-STF tone ina 40 MHz PPDU transmission.

Referring to sub-drawing (b), in case a HE-STF sequence (i.e., 1× HE-STFsequence) for a periodicity of 0.8 μs is mapped to tones of a 40 MHzchannel, the 1× HE-STF sequence is mapped to tones having tone indexesthat are divisible by 16 (i.e., multiples of 16), among the tones havingtone indexes ranging from −240 to 240, and, then, 0 may be mapped to theremaining tones. More specifically, in a 40 MHz channel, among the toneshaving tone indexes ranging from −240 to 240, a 1× HE-STF tone may bepositioned at a tone index that is divisible by 16 excluding the DC.Accordingly, a total of 30 1× HE-STF tones having the 1× HE-STF sequencemapped thereto may exist in the 40 MHz channel.

Sub-drawing (c) of FIG. 13 illustrates an example of a 1× HE-STF tone inan 80 MHz PPDU transmission.

Referring to sub-drawing (c), in case a HE-STF sequence (i.e., 1× HE-STFsequence) for a periodicity of 0.8 μs is mapped to tones of a 80 MHzchannel, the 1× HE-STF sequence is mapped to tones having tone indexesthat are divisible by 16 (i.e., multiples of 16), among the tones havingtone indexes ranging from −496 to 496, and, then, 0 may be mapped to theremaining tones. More specifically, in an 80 MHz channel, among thetones having tone indexes ranging from −496 to 496, a 1× HE-STF tone maybe positioned at a tone index that is divisible by 16 excluding the DC.Accordingly, a total of 62 1× HE-STF tones having the 1× HE-STF sequencemapped thereto may exist in the 80 MHz channel.

FIG. 14 illustrates a 2× HE-STF tone in a per-channel PPDU transmissionaccording to an exemplary embodiment of the present invention. Mostparticularly, FIG. 14 shows an example of a HE-STF tone (i.e., 8-tonesampling) having a periodicity of 1.6 μs in 20 MHz/40 MHz/80 MHzbandwidths. Accordingly, in FIG. 14, the HE-STF tones for each bandwidth(or channel) may be positioned at 8 tone intervals.

The 2× HE-STF signal according to FIG. 14 may be applied to the uplinkMU PPDU shown in FIG. 12. More specifically, the 2× HE-STF signal shownin FIG. 14 may be included in the PPDU, which is transmitted via uplinkin response to the above-described trigger frame.

In FIG. 14, the x-axis represents the frequency domain The numbers onthe x-axis represent the indexes of a tone, and the arrows representmapping of a value that is not equal to 0 (i.e., a non-zero value) tothe corresponding tone index.

Sub-drawing (a) of FIG. 14 is a drawing showing an example of a 2×HE-STF tone in a 20 MHz PPDU transmission.

Referring to sub-drawing (a), in case a HE-STF sequence (i.e., 2× HE-STFsequence) for a periodicity of 1.6 μs is mapped to tones of a 20 MHzchannel, the 2× HE-STF sequence is mapped to tones having tone indexesthat are divisible by 8 (i.e., multiples of 8), among the tones havingtone indexes ranging from −120 to 120, and, then, 0 may be mapped to theremaining tones. More specifically, in a 20 MHz channel, among the toneshaving tone indexes ranging from −120 to 120, a 2× HE-STF tone may bepositioned at a tone index that is divisible by 8 excluding the DC.Accordingly, a total of 30 2× HE-STF tones having the 2× HE-STF sequencemapped thereto may exist in the 20 MHz channel.

Sub-drawing (b) of FIG. 14 illustrates an example of a 2× HE-STF tone ina 40 MHz PPDU transmission.

Referring to sub-drawing (b), in case a HE-STF sequence (i.e., 2× HE-STFsequence) for a periodicity of 1.6 μs is mapped to tones of a 40 MHzchannel, the 2× HE-STF sequence is mapped to tones having tone indexesthat are divisible by 8 (i.e., multiples of 8), among the tones havingtone indexes ranging from −248 to 248, and, then, 0 may be mapped to theremaining tones. More specifically, in a 40 MHz channel, among the toneshaving tone indexes ranging from −248 to 248, a 2× HE-STF tone may bepositioned at a tone index that is divisible by 8 excluding the DC.Herein, however, tones having tone indexes of ±248 correspond to guardtones (left and right guard tones), and such guard tones may beprocessed with nulling (i.e., such guard tones may have a value of 0).Accordingly, a total of 60 2× HE-STF tones having the 2× HE-STF sequencemapped thereto may exist in the 40 MHz channel

Sub-drawing (c) of FIG. 14 illustrates an example of a 2× HE-STF tone inan 80 MHz PPDU transmission.

Referring to sub-drawing (c), in case a HE-STF sequence (i.e., 2× HE-STFsequence) for a periodicity of 1.61 μs is mapped to tones of an 80 MHzchannel, the 2× HE-STF sequence is mapped to tones having tone indexesthat are divisible by 8 (i.e., multiples of 8), among the tones havingtone indexes ranging from −504 to 504, and, then, 0 may be mapped to theremaining tones. More specifically, in an 80 MHz channel, among thetones having tone indexes ranging from −504 to 504, a 2× HE-STF tone maybe positioned at a tone index that is divisible by 8 excluding the DC.Herein, however, tones having tone indexes of ±504 correspond to guardtones (left and right guard tones), and such guard tones may beprocessed with nulling (i.e., such guard tones may have a value of 0).Accordingly, a total of 124 2× HE-STF tones having the 2× HE-STFsequence mapped thereto may exist in the 80 MHz channel.

Hereinafter, a sequence that can be applied to a 1×HE-STF tone (i.e.,sampling at intervals of 16 tones) and a sequence that can be applied toa 2×HE-STF tone (i.e., sampling at intervals of 8 tones) will beproposed. More specifically, a basic sequence is configured, and a newsequence structure having excellent extendibility by using a nestedstructure in which a conventional sequence is used as a parts of a newsequence is proposed. It is preferable that the M sequence that is usedin the following example corresponds to a sequence having a length of15. It is preferable that the M sequence is configured as a binarysequence so as to decrease the level of complexity when being decoded.

Hereinafter, in a state when a detailed example of an M sequence is notproposed, a basic procedure for generating a sequence in variousbandwidths will be described in detail.

Example (A): Example of a 1× HE-STF Tone

The example of the exemplary embodiment, which will hereinafter bedescribed in detail, may generate an STF sequence supporting diversefrequency bandwidths by using a method of repeating the M sequence,which corresponds to a binary sequence.

FIG. 15 illustrates an example of repeating an M sequence.

It is preferable that the example shown in FIG. 15 is applied to 1×HE-STF.

As shown in FIG. 15, when expressed in the form of an equation, the STFsequence for 20 MHz may be expressed as shown in Equation 1.

HE_STF_20 MHz(−112:16:+112)={M}

HE_STF_20 MHz(0)=0   <Equation 1>

The notation of HE_STF(A1:A2:A3)={M}, which is used in Equation 1 andthe other equations shown below is as described below. First of all, thevalue of A1 corresponds to a frequency tone index corresponding to thefirst element of the M sequence, and the value of A3 corresponds to afrequency tone index corresponding to the last element of the Msequence. The value of A2 corresponds to an interval of frequency toneindexes corresponding to each element of the M sequence being positionedbased on the frequency tone interval.

Accordingly, in Equation 1, the first element of the M sequencecorresponds to the frequency band corresponding to index “−112”, thelast element of the M sequence corresponds to the frequency bandcorresponding to index “+112”, and each element of the M sequence ispositioned at 16 frequency tone intervals. Additionally, the value “0”corresponds to a frequency band corresponding to index “0” Morespecifically, Equation 1 has a structure corresponding to sub-drawing(a) of FIG. 13.

As shown in FIG. 15, when expressed in the form of an equation, the STFsequence for 40 MHz may be expressed as shown in Equation 2. Morespecifically, in order to extend the structure of Equation 1 to the 40MHz band, {M, 0, M} may be used.

HE_STF_40 MHz(−240:16:240)={M, 0, M}  <Equation 2>

Equation 2 corresponds to a structure, wherein 15 M sequence elementsare positioned within a frequency band range starting from a frequencyband corresponding to index “−240” and up to a frequency bandcorresponding to index “−16” at 16 frequency tone intervals, wherein “0”is positioned for frequency index 0, and wherein 15 M sequence elementsare positioned within a frequency band range starting from a frequencyband corresponding to index “+16” and up to a frequency bandcorresponding to index “+240” at 16 frequency tone intervals “+16”.

As shown in FIG. 15, when expressed in the form of an equation, the STFsequence for 80 MHz may be expressed as shown in Equation 3. Morespecifically, in order to extend the structure of Equation 1 to an 80MHz band, {M, 0, M, 0, M, 0, M} may be used.

HE_STF_80 MHz(−496:16:496)={M, 0, M, 0, M, 0, M}  <Equation 3>

Equation 3 corresponds to a structure, wherein 15 M sequence elementsare positioned within a frequency band range starting from a frequencyband corresponding to index “−496” and up to a frequency bandcorresponding to index “−272” at 16 frequency tone intervals, wherein“0” (or an arbitrary additional value al) is positioned for a frequencyband corresponding to index “−256”, wherein 15 M sequence elements arepositioned within a frequency band range starting from a frequency bandcorresponding to index “−240” and up to a frequency band correspondingto index “−16” at 16 frequency tone intervals, and wherein “0” ispositioned for frequency index 0. Additionally, Equation 3 alsocorresponds to a structure, wherein 15 M sequence elements arepositioned within a frequency band range starting from a frequency bandcorresponding to index “+16” and up to a frequency band corresponding toindex “+240” at 16 frequency tone intervals, wherein “0” (or anarbitrary additional value a2) is positioned for a frequency bandcorresponding to index “+256”, and wherein M sequence elements arepositioned from “+272” to “+496” at 16 frequency tone intervals.

By applying an additional coefficient to the above-described structuresof Equation 1 to Equation 3, it will be possible to optimize thesequence for PAPR. In case of the related art IEEE 802.11ac system,although it may be possible to extend the predetermined 20 MHz sequencefor the 40 MHz and 80 MHz by using a gamma value, since the gamma valuemay not be applied in the IEEE 802.11ax or HEW system, the PAPR shouldbe considered without considering the gamma value. Additionally, in caseof considering the 1× HE-STF sequence, as shown in Equation 1 toEquation 3, the PAPR should be calculated based on the entire band(e.g., the entire band shown in FIG. 4 to FIG. 6), and, in case ofconsidering the 2× HE-STF sequence, the PAPR should be calculated whileconsidering each unit (e.g., individual units 26-RU, 52-RU, 106-RU, andso on, shown in FIG. 4 to FIG. 6).

FIG. 16 is an example specifying the repeated structure of FIG. 15 inmore detail.

As shown in the drawing, coefficients c1 to c7 may be applied, or(1+j)*sqrt(1/2) may be applied, and additional values, such as a1 anda2, may also be applied.

Based on the content of FIG. 16, an example of the STF sequence that isoptimized for the PAPR is as shown below.

First of all, the M sequence may be determined as shown below inEquation 4.

M={−1, 1, −1, 1, −1, −1, 1, 1, −1, −1, 1, 1, 1, 1, 1,1}  <Equation 4>

In this case, the STF sequence respective to the 20 MHz and 40 MHz bandsmay be determined in accordance with the equations shown below.

HE_STF_20 MHz(−112:16:112)=M*(1+j)/sqrt(2)

HE STF_20 MHz(0)=0   <Equation 5>

HE_STF_40 MHz(−240:16:240)={M, 0, −M}*(1+j)/sqrt(2)   <Equation 6>

The definition of the variables used in the equations presented above isthe same as those used in Equation 1to Equation 3.

Meanwhile, the STF sequence corresponding to the 80 MHz band may bedetermined in accordance with any one of the equations shown below.

HE_STF_80 MHz(−496:16:496)={M, 1, −M 0, −M, 1, −M}*(1+j)/sqrt(2)  <Equation 7>

HE_STF_80 MHz(−496:16:496)={M, −1, M 0, M, −1, −M}*(1+j)/sqrt(2)  <Equation 8>

The definition of the variables used in the equations presented above isthe same as those used in Equation 1 to Equation 3.

The examples shown in Equation 4 to Equation 8, which are presentedabove, may be modified to other examples, as shown below.

First of all, the M sequence that is basically used may be modified asshown in Equation 9.

M={−1, −1, −1, 1, 1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}  <Equation 9>

Equation 9 that is presented above may be applied to all or part ofEquation 5 to Equation 8. For example, it may be possible to use thebasic sequence of Equation 9 based on the structure of Equation 7.

The PAPR for the examples presented in the above-described equations maybe calculated as shown below. As described above, in case of consideringthe 1× HE-STF sequence, the PAPR is calculated based on the entire band(e.g., the entire band shown in FIG. 4 to FIG. 6).

More specifically, the PAPR for the example of applying Equation 4 tothe structure of Equation 5 is equal to 2.33, the PAPR for the exampleof applying Equation 4 to the structure of Equation 6 is equal to 4.40,and the PAPR for the example of applying Equation 4 to the structure ofEquation 7 or Equation 8 is equal to 4.49. Additionally, the PAPR forthe example of applying Equation 9 to the structure of Equation 5 isequal to 1.89, the PAPR for the example of applying Equation 9 to thestructure of Equation 6 is equal to 4.40, and the PAPR for the exampleof applying Equation 9 to the structure of Equation 7 or Equation 8 isequal to 4.53. Although the STF sequences that are presented above showminute differences in the capability of the PAPR, since thecorresponding STF sequences present enhanced PAPR capability as comparedto the related art sequences, it will be preferable to used any one ofthe examples presented above for uplink and/or downlink communication.

Example (B): Example of a 2× HE-STF Tone

It is preferable to apply the example of the exemplary embodiment, whichwill hereinafter be described in detail, to 2× HE-STF.

FIG. 17 illustrates an example of repeating an M sequence.

As shown in FIG. 17, when expressed in the form of an equation, the STFsequence for 20 MHz may be expressed as shown below in the followingEquation.

HE_STF_20 MHz(−120:8:+120)={M, 0, M}  <Equation 10>

As shown in FIG. 17, when expressed in the form of an equation, the STFsequence for 40 MHz may be expressed as shown below in the followingEquation.

HE_STF_40 MHz(−248:8:248)={M, 0, M, 0, M, 0, M}  <Equation 11>

As shown in FIG. 17, when expressed in the form of an equation, the STFsequence for 80 MHz may be expressed as shown below in the followingEquation.

HE_STF_80 MHz(−504:8:504)={M, 0, M, 0, M, 0, M, 0, M, 0, M, 0, M, 0,M}  <Equation 12>

By applying an additional coefficient to the above-described structuresof Equation 10 to Equation 12, it will be possible to optimize thesequence for PAPR. In case of the related art IEEE 802.11ac system,although it may be possible to extend the predetermined 20 MHz sequencefor the 40 MHz and 80 MHz by using a gamma value, since the gamma valuemay not be applied in the IEEE 802.11ax or HEW system, the PAPR shouldbe considered without considering the gamma value.

FIG. 18 is an example specifying the repeated structure of FIG. 17 inmore detail.

As shown in the drawing, coefficients c1 to c14 may be applied, or(1+j)*sqrt(1/2) may be applied, and additional values, such as a1 to a8,may also be applied.

Based on the content of FIG. 18, an example of the STF sequence that isoptimized for the PAPR is as shown below.

First of all, the M sequence may be determined as shown below inEquation 13.

M={−1, 1, −1, 1, −1, −1, 1, 1, −1, −1, 1, 1, 1, 1, 1}  <Equation 13>

In this case, the STF sequence respective to the 20 MHz, 40 MHz, and 80MHz bands may be determined in accordance with the equations shownbelow.

HE_STF_20 MHz(−120:8:120)={M, 0, −M}*(1+j)/sqrt(2)   <Equation 14>

HE_STF_40 MHz(−248:8:248)={M, 1, −M, 0, −M, 1, M}*(1+j)/sqrt(2)

HE_STF_40 MHz(±248)=0   <Equation 15>

HE_STF_80 MHz(−504:8:504)={M, −1, M, −1, M, −1, −M, 0, M, 1, −M, 1, M,1, M}*(1+j)/sqrt(2)

HE_STF_80 MHz(±504)=0   <Equation 16>

The definition of the variables used in the equations presented above isthe same as those used in Equation 1 to Equation 3.

The examples shown in Equation 14 to Equation 16, which are presentedabove, may be modified to other examples, as shown below.

First of all, the M sequence that is basically used may be modified asshown in Equation 17.

M={−1, −1, −1, 1, 1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}  <Equation 17>

The 2× HE-STF sequence for the 20 MHz band may be generated by using amethod of applying Equation 17, which is presented above, to Equation14.

Meanwhile, 2× HE-STF sequence for the 40 MHz band may be generated byusing a method of applying Equation 17, which is presented above, to theEquation shown below.

HE_STF_40 MHz(−248:8:248)={M, −1, −M, 0, M, −1, M}*(1+j)/sqrt(2)

HE_STF_40 MHz(±248)=0   <Equation 18>

Additionally, 2× HE-STF sequence for the 80 MHz band may be generated byusing a method of applying Equation 17, which is presented above, to theEquation shown below.

HE_STF_80 MHz(−504:8:504)={M, −1, M, −1, −M, −1, M, 0, −M, 1, M, 1, −M,1, −M}*(1+j)/sqrt(2)

HE_STF_80 MHz(±504)=0   <Equation 19>

FIG. 19 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 20 MHz band.

Each block shown in FIG. 19 respectively indicates 26-RU, 52-RU, 106-RU,and 242-RU, which are shown in FIG. 4. For example, a first block 1910indicates a leftmost 26-RU, which is shown in FIG. 4, a second block1920 indicates a central 26-RU, which is shown in FIG. 4, a third block1930 indicates a 52-RU, a fourth block 1940 indicates a 106-RU, and afifth block 1950 indicates a 242-RU.

The example of the above-described Equation 13 to Equation 16 may beindicated as example (B-1), and the example of the above-describedEquation 17 to Equation 19 may be indicated as example (B-2). In thiscase, the values indicated in each block represent the PAPRs for example(B-1) and example (B-2), respectively.

FIG. 20 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 40 MHz band. More specifically, eachblock shown in FIG. 20 respectively indicates 26-RU, 52-RU, 106-RU,242-RU, and 484-RU, which are shown in FIG. 5.

FIG. 21 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a left side band of a 80 MHz band. And,FIG. 22 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a right side band of a 80 MHz band. Morespecifically, each block shown in FIG. 21 and FIG. 22 respectivelyindicates 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and 996-RU, which areshown in FIG. 6. In the examples shown in FIG. 21 and FIG. 22, in caseof the 26-RU (i.e., central 26-RU) that is positioned in the DC band,the PAPR of example (B-1) is equal to 1.94, and the PAPR of example(B-2) is equal to 1.94. Additionally, for the entire band, the PAPR ofexample (B-1) is equal to 4.97, and the PAPR of example (B-2) is equalto 5.77.

Example (C): Example of a 2× HE-STF Tone

In case of the 2× HE-STF according to the above-described example (B),due to a collision with a guard band in the 40 MHz band and the 80 MHzband, nulling is required in the tone index “±248” and the tone index“±504”. The following example (C) proposes a STF sequence that does notrequire any nulling to be performed.

FIG. 23 illustrates an example of repeating an M sequence.

As shown in FIG. 23, when expressed in the form of an equation, the STFsequence for 20 MHz may be expressed as shown below in the followingEquation.

HE_STF_20 MHz(−120:8:+120)={M, 0, M}  <Equation 20>

As shown in FIG. 23, when expressed in the form of an equation, the STFsequence for 40 MHz may be expressed as shown below in the followingEquation.

HE_STF_40 MHz(−240:8:240)={M, M, 0, M, M}  <Equation 21>

As shown in FIG. 23, when expressed in the form of an equation, the STFsequence for 80 MHz may be expressed as shown below in the followingEquation.

HE_STF_80 MHz(−496:8:496)={M, M, 0, M, M, 0, M, M, 0, M, M}  <Equation22>

By applying an additional coefficient to the above-described structuresof Equation 20 to Equation 22, it will be possible to optimize thesequence for PAPR. In case of the related art IEEE 802.11ac system,although it may be possible to extend the predetermined 20 MHz sequencefor the 40 MHz and 80 MHz by using a gamma value, since the gamma valuemay not be applied in the IEEE 802.11ax or HEW system, the PAPR shouldbe considered without considering the gamma value.

FIG. 24 is an example specifying the repeated structure of FIG. 23 inmore detail.

As shown in the drawing, coefficients c1 to c14 may be applied, or(1+j)*sqrt(1/2) may be applied, and additional values, such as a1 to a4,may also be applied.

Based on the content of FIG. 24, an example of the STF sequence that isoptimized for the PAPR is as shown below.

First of all, the M sequence may be determined as shown below inEquation 23.

M={−1, 1, −1, 1, −1, −1, 1, 1, −1, −1, 1, 1, 1, 1, 1}  <Equation 23>

In this case, the STF sequence respective to the 40 MHz and 80 MHz bandsmay be determined in accordance with the equations shown below. Sincethe STF sequence for the 20 MHz band is the same as example (B) (i.e.,the same as Equation 14), the indication of the same will be omitted.

HE_STF_40 MHz(−240:8:240)={M, M 0, −M, M}*(1+j)/sqrt(2)   <Equation 24>

HE_STF_40 MHz(−240:8:240)={M, −M 0, M, M}*(1+j)/sqrt(2)   <Equation 25>

HE_STF_80 MHz(−496:8:496)={M, M, −1, M, −M, 1, 0, 1, −M, −M, 1, M,−M}*(1+j)/sqrt(2)   <Equation 26>

The definition of the variables used in the equations presented above isthe same as those used in Equation 1 to Equation 3.

The examples shown in Equation 24 to Equation 26, which are presentedabove, may be modified to other examples, as shown below.

First of all, the M sequence that is basically used may be modified asshown in Equation 27.

M={−1, −1, −1, 1, 1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}  <Equation 27>

The 2× HE-STF sequences for the 40 MHz band and the 80 MHz band may begenerated by using a method of applying Equation 27, which is presentedabove, to the equation shown below. Since the STF sequence for the 20MHz band is the same as example (B), the indication of the same will beomitted.

HE_STF_40 MHz(−240:8:240)={M, −M, 0, M, M}*(1+j)/sqrt(2)   <Equation 28>

HE_STF_40 MHz(−240:8:240)={M, M, 0, −M, M}*(1+j)/sqrt(2)   <Equation 29>

HE_STF_80 MHz(−496:8:496)={M, −M, −1, M, M, −1, 0, −1, −M, M, −1, M,M}*(1+j)/sqrt(2)   <Equation 30>

FIG. 25 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 20 MHz band.

Each block shown in FIG. 25 respectively indicates 26-RU, 52-RU, 106-RU,and 242-RU, which are shown in FIG. 4.

The example of the above-described Equation 23 to Equation 26 may beindicated as example (C-1), and the example of the above-describedEquation 27 to Equation 30 may be indicated as example (C-2). In thiscase, the values indicated in each block represent the PAPRs for example(C-1) and example (C-2), respectively.

FIG. 26 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a 40 MHz band. More specifically, eachblock shown in FIG. 26 respectively indicates 26-RU, 52-RU, 106-RU,242-RU, and 484-RU, which are shown in FIG. 5.

FIG. 27 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a left side band of a 80 MHz band. And,FIG. 28 is a drawing indicating the above-described examples of the PAPRin RU units that are used in a right side band of a 80 MHz band. Morespecifically, each block shown in FIG. 27 and FIG. 28 respectivelyindicates 26-RU, 52-RU, 106-RU, 242-RU, 484-RU, and 996-RU, which areshown in FIG. 6. In the examples shown in FIG. 27 and FIG. 28, in caseof the 26-RU (i.e., central 26-RU) that is positioned in the DC band,the PAPR of example (C-1) is equal to 1.94, and the PAPR of example(C-2) is equal to 6.02. Additionally, for the entire band, the PAPR ofexample (C-1) is equal to 4.99, and the PAPR of example (C-2) is equalto 5.42.

FIG. 29 is a procedure flow chart to which the above-described examplecan be applied.

The example of FIG. 29 may be applied to various transmittingapparatuses, for example, the corresponding example may be applied touser equipments (i.e., non-AP STA).

In step S2910, the transmitting apparatus determines whether to transmita 1× HE-STF signal or to transmit a 2× HE STF signal. For example, inresponse to the trigger frame shown in FIG. 9, in case of transmittingthe uplink PPDU shown in FIG. 12, the transmitting apparatus maytransmit a 2× HE STF signal, and, otherwise, the transmitting apparatusmay transmit a 1× HE STF signal.

In case of transmitting a 2× HE STF, a 2× HE STF signal may be generatedin accordance with step S2920. For example, in case of generating ashort training field (STF) corresponding to a first frequency band(e.g., a 80 MHz band), the STF signal corresponding to the firstfrequency band may be generated based on a sequence wherein apredetermined M sequence is repeated. In this case, the repeatedsequence may be defined as {M, −1, M, −1, −M, −1, M, 0, −M, 1, M, 1, −M,1, −M}*(1+j)/sqrt(2). The M sequence may be the same as M={−1, −1, −1,1, 1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}. In the {M, −1, M, −1, −M, −1, M,0, −M, 1, M, 1, −M, 1, −M}*(1+j)/sqrt(2) sequence, the elementscorresponding to the tone indexes −504 and 504 may be processed withnulling. Additionally, in case of generating a STF corresponding to asecond frequency band (e.g., a 40 MHz band), a {M, −1, −M 0, M, −1,M}*(1+j)/sqrt(2) sequence, and so on, may be used.

In other words, at least any one of the 2× HE-STF signals presented inthe above-described example (B) or example (C) may be used in stepS2920.

In case of transmitting the 1× HE-STF, a 1× HE STF signal may begenerated in accordance with step S2930. In this case, at least any oneof the 1× HE-STF signals presented in the above-described example (A) orexample (C) may be used.

In step S2940, a generated HE-STF signal is transmitted to a receivingapparatus.

FIG. 30 is a block view showing a wireless device to which the exemplaryembodiment of the present invention can be applied.

Referring to FIG. 30, as a station (STA) that can implement theabove-described exemplary embodiment, the wireless device may correspondto an AP or a non-AP station (non-AP STA). The wireless device maycorrespond to the above-described user or may correspond to atransmitting device transmitting a signal to the user.

The AP 3000 includes a processor 3010, a memory 3020, and a radiofrequency unit (RF unit) 3030.

The RF unit 3030 is connected to the processor 3010, thereby beingcapable of transmitting and/or receiving radio signals.

The processor 3010 implements the functions, processes, and/or methodsproposed in this specification. For example, the processor 3010 may berealized to perform the operations according to the above-describedexemplary embodiments of the present invention. More specifically, theprocessor 3010 may perform the operations that can be performed by theAP, among the operations that are disclosed in the exemplary embodimentsof FIG. 1 to FIG. 29.

The non-AP STA 3050 includes a processor 3060, a memory 3070, and aradio frequency (RF) unit 3080.

The RF unit 3080 is connected to the processor 3060, thereby beingcapable of transmitting and/or receiving radio signals.

The processor 3060 may implement the functions, processes, and/ormethods proposed in the exemplary embodiment of the present invention.For example, the processor 3060 may be realized to perform the non-APSTA operations according to the above-described exemplary embodiments ofthe present invention. The processor may perform the operations of thenon-AP STA, which are disclosed in the exemplary embodiments of FIG. 1to FIG. 29.

The processor 3010 and 3060 may include an application-specificintegrated circuit (ASIC), another chip set, a logical circuit, a dataprocessing device, and/or a converter converting a baseband signal and aradio signal to and from one another. The memory 3020 and 3070 mayinclude a read-only memory (ROM), a random access memory (RAM), a flashmemory, a memory card, a storage medium, and/or another storage device.The RF unit 3030 and 3080 may include one or more antennas transmittingand/or receiving radio signals.

When the exemplary embodiment is implemented as software, theabove-described method may be implemented as a module (process,function, and so on) performing the above-described functions. Themodule may be stored in the memory 3020 and 3070 and may be executed bythe processor 3010 and 3060. The memory 3020 and 3070 may be locatedinside or outside of the processor 3010 and 3060 and may be connected tothe processor 3010 and 3060 through a diversity of well-known means.

What is claimed is:
 1. A method in a wireless local area network (LAN)system, the method comprising: generating, by a transmitting station(STA), a short training field (STF) signal based on an STF sequence anda frequency band used for the STF signal, wherein the STF sequence isdefined as {M, −1, M, −1, −M, −1, M, 0, −M, 1, M, 1, −M, 1,−M}*(1+j)/sqrt(2), wherein sqrt( ) denotes a square root, wherein M is asequence having a length of 15 bits and is defined as M={−1, −1, −1, 1,1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}, transmitting, by the transmittingSTA, a packet including the generated STF signal on the frequency bandto a receiving STA.
 2. The method of claim 1, wherein the packet is aphysical protocol data unit (PPDU) and the frequency band is an 80 MHzband.
 3. The method of claim 1, wherein the STF sequence is determinedbased on the frequency band.
 4. The method of claim 1, wherein the STFsequence is configured from a plurality of candidate STF sequences basedon the frequency band, wherein the plurality of candidate STF sequencesare used for different frequency bands.
 5. The method of claim 1,wherein the {M, −1, M, −1, −M, −1, M, 0, −M, 1, M, 1, −M, 1,−M}*(1+j)/sqrt(2) sequence is positioned at intervals of 8 tonesstarting from a lowest tone having a tone index of −504 and up to ahighest tone having a tone index of +504, and wherein elements for toneindexes −504 and 504 in the {M, −1, M, −1, −M, −1, M, 0, −M, 1, M, 1,−M, 1, −M}*(1+j)/sqrt(2) sequence are processed to be null elements. 6.The method of claim 1, wherein elements in the STF sequence are definedin a unit of 78.125 kHz.
 7. The method of claim 1, wherein the STFsequence is used to improve automatic gain control (AGC) estimation intransmission from the transmitting STA.
 8. A transmitting station (STA)of a wireless local area network (LAN) system, comprising: a radiofrequency (RF) unit transmitting or receiving radio signals; and aprocessor controlling the RF unit, wherein the processor is configured:to generate a short training field (STF) signal based on an STF sequenceand a frequency band used for the STF signal, wherein the STF sequenceis defined as {M, −1, M, −1, −M, −1, M, 0, −M, 1, M, 1, −M, 1,−M}*(1+j)/sqrt(2), wherein sqrt( ) denotes a square root, wherein M is asequence having a length of 15 bits and is defined as M={−1, −1, −1, 1,1, 1, −1, 1, 1, 1, −1, 1, 1, −1, 1}, control the RF unit to transmit apacket including the generated STF signal on the frequency band to areceiving STA.
 9. The transmitting STA of claim 8, wherein the packet isa physical protocol data unit (PPDU) and the frequency band is an 80 MHzband.
 10. The transmitting STA of claim 8, wherein the STF sequence isdetermined based on the frequency band.
 11. The transmitting STA ofclaim 8, wherein the STF sequence is configured from a plurality ofcandidate STF sequences based on the frequency band, wherein theplurality of candidate STF sequences are used for different frequencybands.
 12. The transmitting STA of claim 8, wherein the {M, −1, M, −1,−M, −1, M, 0, −M, 1, M, 1, −M, 1, −M}*(1+j)/sqrt(2) sequence ispositioned at intervals of 8 tones starting from a lowest tone having atone index of −504 and up to a highest tone having a tone index of +504,and wherein elements for tone indexes −504 and 504 in the {M, −1, M, −1,−M, −1, M, 0, −M, 1, M, 1, −M, 1, −M}*(1+j)/sqrt(2) sequence areprocessed to be null elements.
 13. The transmitting STA of claim 8,wherein elements in the STF sequence are defined in a unit of 78.125kHz.
 14. The transmitting STA of claim 8, wherein the STF sequence isused to improve automatic gain control (AGC) estimation in transmissionfrom the transmitting STA.